A communication system includes: a plurality of control apparatuses 81 each for controlling packet transmission by one or more communication nodes connected to the control apparatus, by setting a packet processing rule in the communication nodes; and a network information combination apparatus 82 connected to the plurality of control apparatuses 81 and a computation apparatus for computing a packet processing rule across domains each of which indicates a range including one or more communication nodes controlled by a different one of the plurality of control apparatuses 81, and the network information combination apparatus 82 includes: a network information combination unit 83 for acquiring network information on a connection relationship between communication nodes controlled by each control apparatus 81 and combining a plurality of items of network information acquired from each control apparatus 81 based on boundary link information on a connection relationship at a boundary between the domains.